1. Field of the Invention
This invention relates to a thermal image transfer recording medium which has high thermal sensitivity and can yield images with high heat and abrasion resistances, and more particularly to a thermal image transfer recording medium which is suitable for printing images, for instance, on price tags for textile goods.
2. Discussion of Background
Conventionally known thermal image transfer layers or ink layers of thermal image transfer recording media are, for example, (1) a thermal image transfer layer comprising an emulsified resin with a film-formation initiation temperature of 40.degree. C. or more as disclosed in Japanese Laid-Open Patent Application 63-57679; (2) a thermal image transfer layer comprising as the main component a copolymer of styrene, methylmethacrylate and butylacrylate as disclosed in Japanese Laid-Open Patent Application 62-23779; (3) a thermal image transfer layer or ink layer, formed on a transparent protective layer composed of a styrene-methacrylate copolymer and a polyvinyl chloride resin, comprising a mixture of a styrene-methacrylate copolymer, polymethacrylate, a polyvinyl chloride resin, and a coloring agent as disclosed in Japanese Laid-Open Patent Application 62-179992; and (4) a thermal image transfer recording layer, formed on a transparent protective layer comprising a chlorinated polyolefin resin, comprising a (meth)acrylate polymer and a coloring agent as disclosed in Japanese Laid-Open Patent Application 63-42891.
The conventional thermal image transfer recording media comprising the above thermal image transfer layers cannot necessarily yield images having sufficiently high heat resistance, for instance, for printing images on a price tag for clothing. This is because a price tag for clothing is commonly attached to clothing and is heated together with the clothing when the clothing is hot-pressed, and therefore the images printed on the price tag are blurred by the hot pressing. Moreover, in the course of the hot pressing, the ink of the images stains not only the clothing, but also the price tag itself.
More specifically, resins having a film-formation initiation temperature of 40.degree. C. or more, which are used in the above-described thermal image transfer layer (1), are not necessarily highly heat-resistant. Therefore, the thermal image transfer layer of the recording medium, when used in the form of a rolled ribbon, sticks to the reverse side of the support which is in contact with the thermal image transfer layer in the roll at a temperature of approximately 100.degree. C. In other words, the so-called "blocking" occurs. In addition, the images printed on a price tag attached to the clothing by using the recording medium comprising such a resin are blurred and the price tag sticks to the clothing.
An emulsion of a resin having a high glass transition temperature (Tg), such as a polymethyl methacrylate resin, has a high film-formation initiation temperature. Therefore, a recording medium prepared by using such an emulsion in the image transfer layer cannot exhibit high thermal sensitivity. Moreover, images printed on a price tag attached to clothing by using such a recording medium tends to be blurred, and the ink of the images stains both the clothing and the price tag when the clothing is hot-pressed at a temperature of 180.degree. C. or more. The adhesion of the transferred images to an image receiving sheet is so poor that the printed images easily come off the image receiving sheet when rubbed.
Furthermore, when a wax with a low melting point is used as a binder for the thermal image transfer layer, images printed by the recording medium on the price tag are blurred, and both the clothing and the price tag are stained by the ink of the images when the clothing is hot-pressed. Therefore, such a recording medium is not suitable for printing images on price tags for clothing.
When a resin having a high glass transition temperature (Tg) is incorporated in the thermal image transfer layer of (2), (3) or (4), the thermal sensitivity is decreased although the resistance to hot pressing of the images transferred from the layer onto a price tag attached to clothing is improved. On the other hand, by incorporating a resin having a low glass transition temperature (Tg), the thermal sensitivity can be improved, but if such a resin is incorporated, the resistance to hot pressing is significantly reduced.
In addition, when a protective layer comprising a chlorinated polyolefin is employed, images having high resistance to hot pressing cannot be obtained.